A quarter of children in the U.S. were born to unmarried couples who live together, according to latest figures.
Unwed mothers accounted for 40 per cent of babies but today new details emerged about the changing shape of the American family.
About 23 per cent of newborns were to unmarried heterosexual couples who live together - up from 14 per cent in a 2002 study.
Maybe baby: In the past ten years, there has been a sharp rise in couples having children before tying the knot
The Centers for Disease Control and Prevention study was based on interviews with more than 22,000 men and women in the U.S. from 2006 to 2010.
The CDC did not speculate on the reason for the rise but there were suggestions that the cost of a wedding - on average $27,000 - in times of financial hardship and high unemployment could be a cause.
There were a record number of births in America in 2007 - 4.3 million - but that fell to 4 million in 2010.
The demographic of mothers has changed dramatically over the past two decades.
Fluctuating: Although the birth rate has declined in the U.S. since 2007, unmarried couples were accounting for more first-time parents
Women having their first child were now older than in the past - with 14 per cent of babies now born to mothers aged 35 and older compared to 9 per cent in 1990.
The average age of American mothers who had their first baby in 2008 was 25 - a year older than the average first-time mother in 1990.
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